Water contamination of fuel such as petrol, gasoline, and/or middle distillate fuels such as diesel fuel, and jet fuel, is a serious problem. Water contamination can cause corrosion, loss of lubricity, or damage to components of modern engines and fuel systems. Furthermore, water readily freezes in fuel lines, which can have catastrophic consequences if the occurrence takes place, for example, in the fuel lines of aircraft in flight.
To mitigate the risk of this danger two strategies are often employed. The respective strategies are to remove the water from fuel or to add chemical compounds to the fuel which raise the freezing point of water in the fuel. Removal of water from fuel is typically accomplished using a filtration step which often acts via coalescence and separation or by absorption into a polymeric matrix. These technologies are exemplified in coalescer separators used in purification of modern diesel fuel on vehicle or of aviation fuel as described in EI 1550 (Energy Institute Document 1550: Handbook of equipment used for the maintenance and delivery of clean aviation fuel) or by sorbent filter monitors described in EI 1550 and EI 1583 (Energy Institute Document 1583: laboratory tests and minimum performance specifications for aviation fuel filter monitors 6th edition). The other respective strategy of chemical addition is also practiced in the protection of aviation fuels by addition of compounds known in the literature as FSII (fuel system icing inhibitors) to the fuel. The most common compound used for this purpose in jet fuel is known as DIEGME (Diethylene glycol monomethyl ether)
A known solution to accomplish water separation from fuel via absorption is the use of a hydrophilic material which takes up water in the presence of fuel. This hydrophilic water absorbing material is chosen to be non-olefinic to prevent its absorption or swelling by the fuel stream. Furthermore, SAP (super absorbing polymers) for water are found to be much preferred for this application. Herein a super absorbent polymer is defined as a polymer capable of taking up more than its own weight in water on swelling. Due to the swelling behavior of absorbent and super absorbent polymer media in the presence of water, the fuel filters and filter media incorporating these polymers lose permeability as they absorb water swelling at the cost of internal pore volume. This can even result in swelling to the point of flow shutoff if the quantity of water uptake per unit area is large. This behavior forms the basis of the fuel filter monitor, a class of water removal filters that are widely used in aviation today. These fuel filter monitors are tightly specified by the aviation industry as described in standard EI 1583 as specified by the Energy Institute in the U.K. The polymers, filter structures and designs of filter monitors in the prior art are described in U.S. Pat. No. 4,959,141, U.S. Pat. No. 6,997,327 and U.S. Pat. No. 7,998,860 and references therein.
In addition to removing water droplets from a fuel stream, fuel filter monitors provide the specific function of stopping fuel flow or positive flow shutoff when challenged with a water slug or water flow stream. This function is critical for applications where risks of bulk water contamination of fuel could be catastrophic, particularly for aviation operations such as in-flight refueling.
Despite successful commercial application of fuel filter monitors they are known to have significant reported short comings and there is a long felt need for an improved solution. These short comings are well-documented in various reports, test standards, and other documents. Documented examples include the EI 1550 handbook, the EI 1583 test standard, discussion in U.S. Pat. No. 4,959,141, U.S. Pat. No. 6,997,327, product bulletins from manufacturers/distributors of these filter monitors, conference reports on research funded by the US military, and other aviation industry groups. One common issue is that after swelling on exposure to a bulk water slug or water stream, modern monitors may continue to pass fuel or water when exposed to a pressure pulse. U.S. Pat. No. 4,959,141 describes a mechanical solution to this common issue. Another problem is described by U.S. Pat. No. 6,997,327. Specifically, that SAP and their performance can be degraded by water soluble contaminants including polar organic molecules, ethers, and inorganic salts. U.S. Pat. No. 6,997,327 describes a partial solution involving ion exchange nonwovens combined with SAP polymers to deal with the polar and inorganic species which have ionic character.
Another issue of the same nature is that the common FSII anti-icing additive DIEGME is a polar organic molecule as is Biodiesel which is also known as FAME (Fatty Acid Methyl Ester) in the trade. Biodiesel contaminants are commonly introduced into jet fuels in the form of fatty acid methyl ester (FAME) contamination as a result of pipeline transport of biodiesel blends and tail-back phenomenon causing transfer to adjacent or subsequent jet fuel batches. In addition, DIEGME FSII is a common additive to military and arctic aviation fuels worldwide. Currently, all commercial aviation fuel filter monitors sold today rely on SAP technology and possess clear labeling indicating they are incompatible with FSII and DIGEME. This is because exposure of fuel filter monitors to fuel containing FSII can degrade or eliminate their water slug resistance. In addition, there have been several reports of migration of soluble SAP contamination into down stream fuel systems in the presence of fuel containing FSII. Reports range from observation of “apple jelly”, a brown discoloration of fuel treated by monitors to isolation of particles or a gel like substance, identified by chemical analysis as SAP, from FSII contaminated fuel processed through monitors. This contamination has been linked to reported flameouts of jet turbine engines related to clogging of orifices by solubilized SAP particulate from fuel filter monitors which had passed or migrated into the aircraft fuel tanks.
Finally, another drawback of the current fuel filter monitors is that due to swelling of the SAP polymer their performance degrades with progressive water removal. Ultimately resulting in a product which is single-use and which has insufficient permeability for reuse after exposure to water. This results in downtime in applications until such time as the filter monitor can be replaced. Finally, the foreshortened lifetime of filter monitor is an additional burden on the environment due to the generated waste from a filter that must be disposed of prior to fulfilling the filter's expected in use lifetime.
Therefore, it is an object of this invention to address these long-felt needs for a fuel filter monitor which overcomes the aforementioned drawbacks. Specifically, a fuel filter monitor which exhibits improved flow stoppage when challenged with a water stream or slug, particularly when the fuel or water is contaminated with a polar compound. Furthermore, it is an object of the present invention to produce a fuel filter monitor which does not contribute to deleterious and dangerous migration of nonfibrous filter media, in particular SAP particles and solutes, to the fuel down stream of the monitor. Still another object is to produce a fuel filter monitor that can be reused after stopping flow during challenge with water stream or slug.